16 bit transparent Image renders color data on CPU Cycles #70138

New Issue

Jan Lautenschlaeger · 2019-09-21T12:17:34+02:00

2019-09-21 12:17:34 +02:00

System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.02
CPU: Intel i7-4770k

Blender Version
Broken: version: 2.81 (sub 12), branch: master, commit date: 2019-09-20 22:35, hash: 7926e8ea4c
Worked: (optional)

Short description of error
Rendering a transparent Filmic Log 16bit PNG image plane (meaning node color space set to filmic log) with Cycles the CPU renders color data where there should not be any. The GPU works as expected.

Exact steps for others to reproduce the error
every thing with Cycles (have not tested eevee)

render something with transparent background and save as PNG (RGBA, 16bit)
import image as plane ( shadeless )
set image node color space to Filmic log and background to transparent
rendering with CPU or CPU+GPU results in the tiles rendered by the CPU to have color data (see image)

Switch Display Channels to color to see this issue

test.blend

Redner:

on the left is no image plane, only the transparent background

Used image:

**System Information** Operating system: Windows-10-10.0.18362 64 Bits Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.02 CPU: Intel i7-4770k **Blender Version** Broken: version: 2.81 (sub 12), branch: master, commit date: 2019-09-20 22:35, hash: `7926e8ea4c` Worked: (optional) **Short description of error** Rendering a transparent Filmic Log 16bit PNG image plane (meaning node color space set to filmic log) with Cycles the CPU renders color data where there should not be any. The GPU works as expected. **Exact steps for others to reproduce the error** every thing with Cycles (have not tested eevee) 1) render something with transparent background and save as PNG (RGBA, 16bit) 2) import image as plane ( shadeless ) 3) set image node color space to Filmic log and background to transparent 4) rendering with CPU or CPU+GPU results in the tiles rendered by the CPU to have color data (see image) Switch Display Channels to color to see this issue [test.blend](https://archive.blender.org/developer/F7763837/test.blend) Redner: ![render.png](https://archive.blender.org/developer/F7763806/render.png) - on the left is no image plane, only the transparent background Used image: ![test_filmlog.png](https://archive.blender.org/developer/F7763805/test_filmlog.png)

Jan Lautenschlaeger commented

2019-09-21 12:17:34 +02:00

Added subscriber: @Namnak

Steffen Dünner commented

2019-09-23 14:40:54 +02:00

Added subscriber: @SteffenD

Richard Antalik commented

2020-01-13 14:00:45 +01:00

Added subscriber: @iss

Richard Antalik commented

2020-01-13 14:00:45 +01:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Richard Antalik commented

2020-01-13 14:00:45 +01:00

Can not reproduce on ATI GPU

@Namnak Is this still an issue with latest build? https://builder.blender.org/download/

Can not reproduce on ATI GPU @Namnak Is this still an issue with latest build? https://builder.blender.org/download/

Jan Lautenschlaeger commented

2020-01-14 19:20:33 +01:00

Tested it again under blender-2.83-1bcb2bfd5724-windows64 and it still happens.

@iss It has nothing to do with the GPU; the white squares are the CPU render tiles. GPU tiles are (as can be seen) correct, i.e. no/ black color (RGB) data and full alpha.

But seen that it is a super edge case and because it behaves as expected in normal renders (e.g. when the image plane is in front of other geometry), not sure if it is worth fixing (now).

G channel, image plane in front of geometry

Further tested the saved RGBA PNG file (see below) by opening it in a new blender instance and in Affinity Photo. Interestingly the blender compositer still shows the squares in the color channels. Affinity does not.

Tested it again under blender-2.83-1bcb2bfd5724-windows64 and it still happens. @iss It has nothing to do with the GPU; the white squares are the CPU render tiles. GPU tiles are (as can be seen) correct, i.e. no/ black color (RGB) data and full alpha. But seen that it is a super edge case and because it behaves as expected in normal renders (e.g. when the image plane is in front of other geometry), not sure if it is worth fixing (now). ![Unbenannt.PNG](https://archive.blender.org/developer/F8278150/Unbenannt.PNG) - G channel, image plane in front of geometry Further tested the saved RGBA PNG file (see below) by opening it in a new blender instance and in Affinity Photo. Interestingly the blender compositer still shows the squares in the color channels. Affinity does not. ![untitled_+Cube+SkyColor1.png](https://archive.blender.org/developer/F8278162/untitled__Cube_SkyColor1.png)

Richard Antalik commented

2020-01-14 22:35:26 +01:00

Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'

Richard Antalik commented

2020-01-14 22:35:26 +01:00

@Namnak Thank you for additional information. Sorry I am not sure if I didn't accidentaly copied this "auto-reply" from another thread (lots of fairly old reports to go through).

I tested this, and couldn't see the difference between CPU and GPU render. But now I am looking at this closer, I see that in your render both black and white tiles are fuly opaque, while my render is transparent.

Can you tell us what compute you used (CUDA / OpenCL)? this is not stored in .blend file.

As to whether this is bug or not, I will leave to developers that are involved in rendering.

@Namnak Thank you for additional information. Sorry I am not sure if I didn't accidentaly copied this "auto-reply" from another thread (lots of fairly old reports to go through). I tested this, and couldn't see the difference between CPU and GPU render. But now I am looking at this closer, I see that in your render both black and white tiles are fuly opaque, while my render is transparent. ![untitled.png](https://archive.blender.org/developer/F8278404/untitled.png) Can you tell us what compute you used (CUDA / OpenCL)? this is not stored in .blend file. As to whether this is bug or not, I will leave to developers that are involved in rendering.

Jan Lautenschlaeger commented

2020-01-20 20:36:57 +01:00

Can you tell us what compute you used (CUDA / OpenCL)?

I'm rendering with CUDA (GTX 1080ti).

Sorry, maybe I was not clear in describing the "problem".
As you said, the final render looks completely correct, but looking at the R, G or B channel of the final render individually (by selecting them from the small menu in the top right corner) it can be noticed, that the transparent parts of the image plane are rendered white on CPU (and apparently ATI GPUs), while CUDA GPUs render black.

I have added my render to the file and selected the B color channel. Maybe this helps.

test_v2.blend

As mentioned before, this is only a problem when the final render has to be separated into the RGB(A) companies or when it gets saved as a JPEG image (because no support for alpha).

> Can you tell us what compute you used (CUDA / OpenCL)? I'm rendering with CUDA (GTX 1080ti). Sorry, maybe I was not clear in describing the "problem". As you said, the final render looks completely correct, but looking at the R, G or B channel of the final render individually (by selecting them from the small menu in the top right corner) it can be noticed, that the transparent parts of the image plane are rendered white on CPU (and apparently ATI GPUs), while CUDA GPUs render black. I have added my render to the file and selected the B color channel. Maybe this helps. [test_v2.blend](https://archive.blender.org/developer/F8290336/test_v2.blend) As mentioned before, this is only a problem when the final render has to be separated into the RGB(A) companies or when it gets saved as a JPEG image (because no support for alpha). ``` ```

Richard Antalik commented

2020-01-20 21:18:15 +01:00

Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'

Richard Antalik commented

2020-01-20 21:18:15 +01:00

Thanks for additional info.

I can confirm this even on openCL.

Thanks for additional info. I can confirm this even on openCL.

Brecht Van Lommel commented

2020-05-14 02:27:52 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2020-05-14 02:27:52 +02:00

There's a tiny precision difference between CPU and GPU, rendering pixels with 0.0 and 0.0005 alpha. This shows up significantly when inspecting the Color alone, but this is more of an artifact of Blender dividing out the alpha than an actual significant difference if you'd use save or use this render for compositing.

Philipp Oeser removed the

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16 bit transparent Image renders color data on CPU Cycles #70138